1. Field of the Invention
This invention relates to a scale device used for detecting the position of a straight line in machine tools or in industrial machines by way of relative position detection.
2. Related Art
This type of the scale device is composed in general of a base unit, having a graduated scale secured to a base member, and a slider unit, mounted relatively slidably on this base unit and carrying a sensor adapted for detecting the graduations recorded on the scale.
In this type of the conventional scale device, a scale in the shape of a round rod is provided as the scale on the base unit side, and a detection head unit having a sensor for detecting the graduations is provided on the slide unit side. The above-described scale is slidably inserted in an opening in the detection head unit. There is also provided a universal mechanism in the detection head unit to permit mounting tolerances and tolerances for component parts.
Among these scale devices, there is such a scale device employing a thin-sheet-like scale as the graduated scale.
The scale device, employing the thin-sheet-like scale, is combined with another member over the entire length, or uses an auxiliary cushioning member, for supporting the scale.
However, with the scale device of the structure in which the round-rod-like scale is inserted in the opening in the detection head unit, the telescopic movement of the detection head unit relative to the scale cannot be realized except from the end face side of the scale, thus worsening assembling and maintenance characteristics. Also, the detection head unit needs to be provided with a complicated universal mechanism in order to cope with position changes to allow for mounting and manufacturing tolerances, thus leading to increased cost.
If, in a scale device employing a thin-plate-like scale, the thin-plate-like scale has a temperature expansion coefficient different from that of the member supporting the thin-plate-like scale, the scale and the supporting member undergo differential deformation thus worsening measurement accuracy. Moreover, since separate members are used, the problem of increased cost is raised inevitably.